Many kinds of devices need to be protected from various ambient substances, such as water vapor or oxygen, by means of a package in order to achieve an acceptable device lifetime. Such devices needing to be protected include, for example, electronic components, such as organic light-emitting diodes (OLEDs) and micro-electro-mechanical systems (MEMS).
In the cases when the devices to be protected are rigid and can be packaged in a rigid package, a sufficiently gas-tight package is typically realized by providing the package in the form of impermeable base and lid parts, which are bonded together following placement of the device to be protected on the base.
When, however, the devices to be protected are flexible, the package is typically also required to be flexible. Several approaches have been tried to achieve a flexible package which has a sufficiently low leakage rate with respect to one or several particular ambient substances to obtain an acceptable device lifetime.
According to one approach, one or several layers of inorganic coatings are deposited on the bottom side of the flexible substrate on which the device to be protected is mounted, and on top of the device. However, these coating have so-called pinholes, which allow penetration of ambient substances, such as moisture and oxygen.
According to another approach, as disclosed in, for example, JP 2001-118674, an OLED is mounted on a flexible transparent multi-layer substrate which is treated to prevent moisture and air from penetrating the substrate and reaching the OLED through the substrate. In order to enclose the OLED, a closure film, comprising a metallic foil layer and an insulator layer is fixed to the substrate around the OLED by means of an adhesive. Subsequently, the closed space formed by the substrate with mounted OLED and the closure film is evacuated and sealed so that the OLED is vacuum-packed. In order to adsorb moisture entering the package through the substrate and/or the closure film, a drying-agent layer is provided on the inside of the closure film.
Such a package is, however, not an optimal solution, since a large number of inorganic/organic layers are typically required to obtain a sufficiently low leakage rate through the package. A production process for producing such a virtually pin-hole free multi-layer structure is typically sensitive and requires that the formation of the different layers takes place in a clean-room in order to obtain an acceptable yield. Consequently, such a multi-layer structure is costly to manufacture, while still exhibiting an insufficient leakage performance.
Accordingly, there is a need for an improved and/or more cost-efficient package for protecting a device from ambient substances.